1. Field of the Invention
The present invention relates generally to three dimensional fabrics, and more particularly, it relates to a method of producing a fabric reinforcing matrix for composites.
2. Description of the Related Art
Fabric reinforcing composites are commonly used as light structural materials. A three-dimensional fabric is conventionally used as a reinforcing matrix for a composite. A three-dimensional fabric generally includes three kinds of threads or yarns respectively extending along the X, Y and Z directions. Composites having such a three-dimensional fabric as a frame member, are expected to be widely used as structural materials for rockets, aircraft, automobiles, marine vessels and buildings. The frame member is impregnated with a resin or other inorganic substances. The use of five-axis three-dimensional fabrics, having yarns that are angularly arranged with respect to the longitudinal direction, is proposed. These yarns are provided in addition to the yarns extending along the X, Y and Z directions.
An exemplary method of producing a three-dimensional fiber structure is to laminate a plurality of yarn layers, each formed by arranging lines of yarn repeatedly looped back at both ends, and to interconnect these yarn layers by the lines of yarn running in the thickness (vertical) direction. Such a method is disclosed in Japanese Unexamined Patent Publication No. Sho 63-42955. As shown in FIG. 29, of the present application, this Japanese publication describes apparatus that utilizes a plurality of yarn guide pipes 32 that are placed upright at predetermined pitches on a base plate 31.
Plate-like separators 33 are placed in parallel between the yarn guide pipes 32. A plate-like spacer 34 lies on, and extends perpendicularly to the separators 33. The lines of the first endless yarn Y1 are looped back and engage with the yarn guide pipes 32 located at the peripheral portions of the base plate 31. The lines of the first endless yarn Y1 also weave between the yarn guide pipes 32 in a direction perpendicular to the direction of the arrangement of the spacer 34, yielding a yarn layer.
The lines of the first endless yarn Y1 are arranged on the yarn layer and are looped back in a direction perpendicular to the direction of arrangement of the first endless yarn. The arrangement of the first endless yarn Y1 is repeated in the same manner to provide a lamination of a predetermined number of yarn layers, thus yielding a yarn lamination. Next, a spacer 34 is placed on the yarn lamination in the same manner as described above. The yarn lamination is then tightened by the spacers 34 from the top and bottom directions. Then, the yarn guide pipes 32 are replaced with the lines of the second endless yarn Y2, for completing a reinforcing matrix for the composite.
The yarn guide pipes 32 are replaced with the lines of the second endless yarn Y2 in the following manner. First, the separators 33 are removed in order, and the yarn guide pipes 32 are pulled up in succession to the vicinity of the lower spacer 34. Then, the second endless yarn Y2 is bent in a loop (L), and is hooked on a yarn guide 35, which in turn, is inserted into the associated yarn guide pipe 32. Then, the yarn guide pipe 32 is pulled up so that the loop L comes out on the top of the lamination of the first endless yarn Y1. In this condition, the loop L is removed from the yarn guide pipe 32 and the third endless yarn Y3 is inserted as a tacking yarn through the loop L. Then, the second endless yarn Y2 is pulled down to tighten the yarn lamination. The foregoing steps are repeated each of the yarn guide pipes 32, to complete the replacement of the yarn guide pipes 32 with the lines of the second endless yarn Y2.
In the above method, the yarn lamination is tightened by the cooperation of the lines of the second endless yarn Y2 for coupling the yarn lamination, and the lines of the third endless yarn Y3, which are inserted through the loops L of the endless yarn Y2. The direction of arrangement of the lines of the second endless yarn Y2 on the opposite surface of the yarn lamination to the one where the lines of the third endless yarn Y3 are arranged, is the same as the direction of arrangement of the third endless yarn Y3.
Accordingly, the yarn lamination is firmly tightened at those portions where the lines of the second endless yarn Y2 face the lines of the third endless yarn Y3. As a result, the portions between the tightened portions will rise, causing the yarn lamination to undulate. In other words, the yarn lamination does not have a uniform thickness. This not only causes a periodic variation in the fabric filling factor, but also shortens the length of the reinforcing matrix along the direction perpendicular to the direction of arrangement of the lines of the third endless yarn Y3. Therefore, the intended three-dimensional fiber structure will not be obtained.
In impregnating such a three-dimensional fiber structure with resin, if this structure were not simultaneously pressed and stretched in the direction perpendicular to the undulation, the variation in the fabric filling factor is transmitted directly to the composite and the final product.
In order to provide a large reinforcing matrix, more than ten thousand yarn guide pipes 32 might be needed. Consequently, it would be difficult to replace the yarn guide pipes 32 one by one, with a single second endless yarn Y2.
Further, in the above method, the yarn guide pipes 32 serve as means through which the lines of the second endless yarn Y2 are inserted, and the second endless yarn Y2 is inserted into the yarn lamination at the same time as the associated yarn guide pipe 32 is removed. This method however requires that the yarn guide pipes 32 be pulled from the opposite side to the inserting side of the yarn guide 35. This will not cause any problem when the reinforcing matrix for composite is of a flat type, but will be inconvenient when the reinforcing matrix is U shaped, box shaped, or with narrow spaces between the opposite faces. This is because when the yarn guide pipe 32 is driven out from one side toward the opposite side, the yarn guide pipe 32 might encounter the opposite surface and might not be removed. Further, in pulling the yarn guide pipe 32 in the direction away from the opposite surface, it would be troublesome to insert the yarn guide 35 with the second endless yarn Y2 hooked thereon, into the associated yarn guide pipe 32.
Japanese Patent Publication Sho 61-30059 discloses a method of sewing a plurality of laminations of two-dimensional yarn layers with a sewing machine to produce a three-dimensional fiber structure. The sewing machine used in this method is equipped with an auxiliary needle 37 in addition to a sewing needle 36, as shown in FIG. 30 at the present application. The lamination of yarn layers 38 is stitched with a sewing yarn 39 and a shuttle yarn 40. The auxiliary needle 37 pierces the yarn layers 38 before the sewing needle 36, to facilitate the insertion of the sewing needle 36.
As the plurality of laminations of two-dimensional yarn layers are sewn together using the sewing machine, it is unnecessary to replace yarn guide pipes or pins with the coupling yarn. The fabric materials that are used in a reinforcing matrix are glass fiber, carbon fiber, ceramic fiber and the like, which do not stretch very much, and which are generally fragile. At the time the auxiliary needle 37 pierces the dense fiber structure, the needle 37 is likely to damage part of the fiber stricture. In addition, it is difficult to secure sufficient space for the sewing needle 36 with the sewing yarn 39 inserted through its eye, to be smoothly inserted into the space formed by the auxiliary needle 37. Thus, when the sewing needle 36 pierces the fiber structure, it is likely to damage the fiber structure again.
Another method of producing a three-dimensional fabric has also been used. In this method, the yarn is placed between regulating members (pins) arranged at predetermined pitches on the base, and is looped back at the edges of the base, forming a lamination. The pans are replaced with vertical yarns using replacing members which hold coupling yarns (vertical yarns). In this case, the pins and the yarn lamination are removed from the base before the replacement operation. Then, the replacing member is placed on the associated pin and is pressed to drive out the pin and, at the same time, to insert the vertical yarn into the space formed by the pin. When the pins are removed from the base, however, both ends of each pin become free, so that the pins could tilt under the pressure of the laminated yarn layers. At this time, positions of the tips of the pins are not stable, thus making it difficult to mechanically abut the replacing members on the pins. It is therefore difficult to perform automatic replacement with a machine without misplacement of the vertical yarn.